Is it normal for stutterers to be able read out loud quickly with no problem?

Is it normal for stutterers to be able read out loud quickly with no problem? I just started stuttering when talking to friends. I also noticed it talking to my brother over the phone. Usually in the middle of a sentence. I was curious and tried reading outloud by myself and I'm able to read at very quick speeds without any problem at all. Would this suggest the issue is some social anxiety? (As opposed to a medical issue) I'm just trying to narrow down what might be causing this sudden onset of stuttering.